will not be forgotten. A cutout pro- 
vides a place for the stack of 60. 
After irradiation the slides are re- 
moved, developed and read. The four- 
teen slides across the tray tel] us whether 
(a) the scan width is adequate to cover 
the product, (b) the dose is right, (ce) 
the dose is aeceptably uniform within 
the scan width. From the stack, we 
get the depth of useful penetration. 
The procedure is similar for the 2- 
Mev Van de Graaff machine except 
that only four slides are needed for scan 
width and 20 for penetration. 
As a spot check for dose, a single 
slide on plywood in the center of a tray 
is sent through the conveyor system 
every hour. 
Product monitoring. A rigid vinyl 
slide is placed under the product in the 
direction of travel, on each tray. The 
slides are numbered consecutively, and 
the numbers also identify the trays. 
The slides are removed after irradiation, 
developed and read at their lightest 
point. Only if this reading indicates a 
sterilizing dose is the tray released for 
sterility sampling. Otherwise the 
material has to be salvaged. 
Package Design 
We are now packaging our radiation- 
sterilized sutures in the aluminum-foil 
packages shown on the cover, on page 
87 and in Fig. 5. We devoted a great 
dea] of effort to investigation of alumi- 
num-foil-plastic laminates. The re- 
sulting package is impermeable, at- 
tractive, and easy to open by tearing. 
It takes irradiation well. An apparent 
disadvantage is that it is opaque. 
However, our field evaluation showed 
that there is no preference for a trans- 
parent package. Ease of opening and 
good identification are found much 
more important. 
Our first packaging ideas revolved 
around plastics because they are trans- 
parent like glass tubes. We deter- 
mined the irradiation characteristics of 
a large number of plastic films. Simul- 
taneously we studied the permeabilities 
of these films. We had to select a 
plastic that could withstand irradiation 
and, more importantly, that was imper- 
meable to the fluids inside and outside 
the package. Inside the package is 
90 % isopropy] alcohol to make the cat- 
gut pliable. The packages are stored 
in a jar containing 97 % isopropyl alco- 
hol and 1% formaldehyde. This stor- 
age solution is intended to sterilize and 
to maintain the sterility of the outside 
148 
of the packages. Any significant pene- 
tration of formaldehyde to the inside 
will destroy the catgut. Kel-F 500 
was the only plastic film that satisfied 
our strict requirements, and it proved 
too expensive. 
What Does It Cost? 
While it is difficult to adjust cost 
figures from one irradiation operation 
to another, the elements of cost can be 
identified and some rough estimates 
can be made. 
Capital costs are high. Available 
accelerators range from about $50,000 
to nearly $200,000 depending primarily 
on power output. Monitoring and con- 
trol equipment can range from as low as 
$5,000 to as high as $75,000. Finally 
the facility costs will depend on the 
FIG. 5. OPENING NEW PACKAGE is 
quick, easy and safe. There is no 
glass to cut the nurse or contaminate the 
operative field 
type of construction and the space re- 
quirements. In turn, the space re- 
quirements and type of construction 
depend on accelerator type. For in- 
stance, a 3-Mev Van de Graaff ma- 
chine requires a minimum of 20 X 25 ft 
with at least 30 ft vertical headroom. 
A modern linae requires much less 
space, particularly in the vertical 
direction. 
The principal operating expenses are 
labor and maintenance. A single ac- 
celerator needs a competent technician 
for operation and at least one addi- 
tional technician to assist in mainte- 
nance. Additional labor is required 
for loading and unloading the product 
on conveyor belts. 
Maintenance and repair costs vary 
with the type of accelerator. Probably 
the highest cost is experienced with the 
linear accelerator and will average 
about $12.50 per operating hour. This 
includes only replacement parts. Most 
of our linac breakdowns are associated 
with failures of high-voltage diodes, 
thyratrons and klystrons. The accel- 
erator tube can cause trouble if mis- 
aligned or if the beam is not properly 
focused. Generally the repairs take 
from a few minutes to a couple of hours. 
Vacuum troubles take one or two days, 
but they happen very seldom. 
Shutdowns on the Van de Graaff are 
mainly caused by loosening or break- 
down of the belt, breakdown of belt 
spacers or equipotential rings. Shut- 
downs are very infrequent, but they 
require one day for repairs because the 
tank has to be removed in each case. 
Electron-beam sterilization is not 
cheap. However, it is unfair to make 
direct cost comparisons between elec- 
tron-beam sterilization and other forms 
of sterilization. Some objects can be 
sterilized only by electron beam. 
Newer forms of packaging may be 
possible only with this new method of 
sterilization. 
Developments now under way in 
high-frequency amplifiers promise a 
major reduction in both initial and 
operating costs. This plus the cost 
advantages of mechanization may well 
bring the cost of radiation sterilization 
to that of heat. 
Safety 
Our whole installation is designed for 
maximum safety. Shielding is ade- 
quate for nearly complete absorption of 
aJl radiation. The doors leading to the 
target and accelerator rooms are locked 
and interlocked with the machine. 
Opening of any of these doors will turn 
off the machine instantaneously. 
When the machine is turned on, there is 
a delay in starting up. During this 
delay a horn sounds repeatedly to warn 
people that irradiation is about to begin. 
Through a maze-and-mirror system, 
the target room can be easily inspected. 
The highest radiation Jevel we have 
detected in any area occupied by per- 
sonnel is less than 0.5 mr/hr. Under 
normal operating conditions the radi- 
ation level is about one tenth of this. 
BIBLIOGRAPHY 
1. R. E. Pepper, N. T. Buffa, V. L. Chandler. 
Relative resistances of microorganisms to 
cathode rays, III. Bacterial spores, Appl. 
Microbiol. 4, 150 (1956) 
. Linear accelerators gain in use as radiation 
facilities, NUCLEONIcS 14, No. 11, 166 (1956) 
3. J. Weiss. Chemical dosimetry using ferrous 
and ceric sulfates, NUCLEONIcS 10, No. 7, 28 
(1952) 
4. E. J. Henley. Gamma-ray dosimetry with 
cellophane-dye systems, NUCLEONICS 12, No. 9, 
62 (1954) 
5. C. Artandi, A. A. Stonehill. Polyvinyl chlo- 
ride—new high-level dosimeter, NUCLEONICS 
16, No. 5, 118 (1958) 
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